Radio frequency set



May 21, 1929. J. c. SNELL RADIOFREQUENCY SET Filed June 6, 1925 M vmw mmummmmMM Patented May 21, 1929.

UNITED STATES 1,714,326 PATENT OFFICE.

iTAMES C. SNELL, F OAK PARK, ILLINOIS, ASSIGNOR TO PREMIER ELECTRIC COM- ."PANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

RADIO FREQUENCY SET.

Application filed June 6, 1925. Serial No. 85,447.

The invention relates to radio frequency sets.

One object of the invention is to provide an improved tuned radio frequency amplification receiving system, in which provision is made for not only suppressing free oscillations in the circuit ensemble, but also for controlling the transference of oscillations from one individual grid-circuit to another.

Another object of the invention is to provide means for this purpose which is combined with transformers in the circuits of the system.

A further object of the invention is to pro vide a unitary structure in which is included the transformer and the resistance for oscillation control between the individual circuits of the system.

The invention consists in the several novel features hereinafter set forth and more particularly defined by claims at the conclusion hereof.

In the drawings: Fig. 1 is a diagram of a radio receiving system with a two-step tuned radio frequency amplification and detector circuits. Fig. 2 is a longitudinal section of the combined transformer and resistance used in the grid-circuits, and Fig. 3 is a cross-section thereof.

The invention is exemplified in a tuned radio frequency system with two stages of amplification and a detector, although it will be understood that it may be embodied in a system with any desired number of stages of amplification. The system includes antenna8 connected to a conductor 4:, in which .the primary winding 5 of a transformer 6 is included, a detector rheostat 30, to which said conductor is connected, and a conductor 31, which is connected to ground at 17. Each stage includes a transformer 6 comprising a primary winding 5 and a secondary winding 7, and an audion tube 3 comprising a grid 10, a plate 12, and a filament 15. The B battery 9 (usually 90 volts) has its positive side connected by a branched conductor 9 to the primary windings 5 of the transformers 6 between the amplifying stages, and each of said windings is connected by a conductor 9'' to one of the plates 12. One end of each secondary winding 7 is connected by a conductor 11 to its rid 10, and the other end is connected t rough a resistance winding 33 to a com- .ductor 26, to

men conductor 4 The positive side of the A battery 16 (usually six volts) is connected by a branched conductor 28 to the positive terminal of each of the filaments 15. The negative terminal of each filament 15 is connected by a branch conductor 26 and a common conductor 31 to the negative side of battery 16. A rheostat 25 is included in conprovide variable resistance in the filament circuit. Each stage also includes a variable condenser 18 in a conductor 19, between conductors 4 and 11.

The detector tube 3 includes a grid 10 connected by a conductor 11 to one end of the secondary coil 7 of the transformer 6, which has its primary winding 5 connected to the plate 12 of the second stage, a filament 15, which has its positive terminal connected by conductor 28, to battery 16, and a plate 12, which is connected by a conductor 21 in which the receiver, such as a telephone or loud speaker 22, is included, to a contact 23, which is connected to receive the desired voltage from the battery 14. A suitable grid leak 40 is in a shunt wire 41.

In practice, it has been found that in tuned radio frequency amplification, variable or fixed high resistance, such as a potentiometer (which should be non-inductive to avoid shifting dial settings) connected to the common grid return ground conductor, may suppress free oscillations in the circuit ensemble, but it does not oppose the transference of oscillations from one grid circuitto another, and consequently the circuit ensemble is not controllable at its efficient point, and that the introduction of a low resistance into each of the individual radio frequency grid circuits dampens or suppresses the transference of oscillations from one individual grid circuit to another. B inclusion of low resistance in the individual grid circuits, when accurately proportioned, superior amplification is obtained. For this purpose, a low resistance inductance winding 33 (say 6 ohms) is connected to one end of the secondary coil of each of the transformers 6, which may have, say 12 ohms resistance. By including this resistance as a part of the transformer, and by winding it inductively as a part of the total correct secondary inductance, it has no shifting effect on the dial settings and, furthermore the transformer and resistance can be readily installed as units in the system. In Fig. 2, there is exemplified a transformer for this shell 39.

In low wave lengths, more resistance is required in the grid circuits, than in the high waves and, therefore, only a part of the total resistance required for the reception of 10W leingths, say 6 ohms, is lncluded in the resistance in the transformer, and the detector filament rheostat 30 serves as an additional variable grid-circuit resistance for all the grid-circuits, so that the resistance can be reduced at will to fit the station tuned in. By thus using the detector rheostat, an additional control knob, as is necessary in all tuned radio frequency circuits, in which oscillation is controlled by means of potentiometer, is avoided. By this method of oscillation control, it is possible to adjust the circuit up to the oscillation point or point of highest efiiciency, and also to prevent it from gettinginto free oscillation without sacrificing any appreciable efficiency, such as is the case in circuits employing other means to control these oscillations. It has been found that the system described has uniform high efficiency on all wave lengths.

The invention exemplifies a tuned radio frequency receiving system, in which the transference of oscillations from one individual grid-circuit to another is prevented;

in which the circuit ensemble is controllable at its point of greatest efiiciency; in which the resistance in the, individualcircuits is vincluded'asa part of the transformer unit,

so that it may be readily installed; and in which the detector rheostat is utilized as an additional variable grid-circuit resistance to adjust the circuit up to the oscillation point or point of highest efficiency for different wave lengths to prevent free oscillation, without sacrificing any appreciable efficiency in the system.

The invention is not to be understood as restricted to the details set forth, since these may be modified within the scope of the appended claims, without departmg from the spirit and scope of the invention.

Having thus described the invention, what I claim as new and desire to secure .by Letters Patent, is: 1

1. A transformer for tuned radio frequency receiver systems comprising a core,

a primary winding on the core, a secondary winding on the core, and a resistance winding composed of a material of higher resistance than that of the secondary winding on the core and connected to the secondary winding and forming a continuation thereof.

2. A radio frequency transformer including primary and secondary windings in one of which a resistance is included as a continuation thereof and supplying a part of the inductance of such winding.

3. A radio frequency transformer including primary and secondary windings one of which is composed of two types of wire, one type of wire being standard copper current conductor and the other forming acontinuation thereof, being of a material to offer more than the usual conductor resistance.

Signed at Chicago, Illinois, this 27th day of May, 1925.

JAMES C. SNELL. 

